EFFECTS OF DIPALMITOYLGLYCEROL AND FATTY-ACIDS ON MEMBRANE-STRUCTURE AND PROTEIN-KINASE-C ACTIVITY

The individual and combined effects of the saturated diacylglycerol (D AG) dipalmitin (DP) and saturated or polyunsaturated unesterified fatt y acids (PUFAs) on both the structure of phosphatidylcholine/phosphati dylserine (PC/PS; 4:1 mol/mol) bilayers and on protein kinase C (PKC) activity were studied using H-2 nuclear magnetic resonance (NMR) and e nzyme activity assays. In the absence of DP, PUFAs only slightly activ ated PKC whereas palmitic acid had no effect. In the absence of fatty acids, DP induced lateral phase separation of the bilayer into liquid- crystalline and gel phases. Under these conditions virtually all DP wa s sequestered into the gel phase and no activation of PKC was observed . The addition of polyunsaturated arachidonic or docosahexaenoic acids to the DP-containing bilayers significantly increased the relative am ounts of DP and other lipid components in the liquid-crystalline phase , correlating with a dramatic increase in PKC activity. Furthermore, t he effect was greater with PS, resulting in an enrichment of PS in the liquid-crystalline domains. In the presence of DP, palmitic acid did not decrease the amount of gel phase lipid and had no effect on PKC ac tivity. The results explain the observed lack of PKC-activating capaci ty of long-chain saturated DAGs as due to the sequestration of DAG int o gel domains wherein it is complexed with phospholipids and thus not available for the required interaction with the enzyme.